Self-sustained electrical discharges are utilized to excite high pressure gas lasers and to generate an ionized plasma for certain types of chemical reactors. It has been found that glow discharges that are stabilized against arcing and have a homogeneous volume distribution perform more efficiently in the excitation of lasers and in various other electrical discharge applications. A variety of techniques have been utilized to provide an initial discharge gap ionization which will allow initiation of a uniform glow discharge, including photoionization of gas molecules in the main discharge gap by ultraviolet light, photoelectron ejection from the cathode material by ultraviolet light, or direct injection of free electrons from an area outside the discharge gap. Typically, devices which provide preionization in the foregoing ways utilize a preionizer supplied by a separate energy delivery circuit, which is fired to provide the ionizing photons or electrons to the main discharge gap before the main pulse is applied across the gap.
In present preionizer structures, the ultraviolet light is usually derived from the production of bare sparks near or adjacent to the main discharge volume. Producing these intense sparks usually requires a substantial expenditure of energy and frequently results in the contamination of the main discharge gap volume by chemical products associated with the sparks themselves, or with the heating of the adjacent supporting structures by the sparks.
In addition to their utility in pulsing lasers, electrical discharges are also employed in some types of chemical reactors such as ozone generators. Ozone generators typically utilize a pair of spaced electrodes which extend linearly in an enclosure through which air is passed. Application of a high voltage between the electrodes of the ozone generator usually results in a linear array of sparks rather than a uniform glow discharge. Over a period of time, the sparks tend to pit and damage the electrodes, and the quantity of ozone produced per energy applied by spark discharges is generally less than can be obtained with uniform glow discharges.